Dual Requirement for the EcR/USP Nuclear Receptor and the dGATAb Factor in an Ecdysone Response in Drosophila melanogaster

Abstract

The EcR/USP nuclear receptor controls Drosophilametamorphosis by activating complex cascades of gene transcription in response to pulses of the steroid hormone ecdysone at the end of larval development. Ecdysone release provides a ubiquitous signal for the activation of the receptor, but a number of its target genes are induced in a tissue- and stage-specific manner. Little is known about the molecular mechanisms involved in this developmental modulation of the EcR/USP-mediated pathway. Fbp1 is a good model of primary ecdysone response gene expressed in the fat body for addressing this question. We show here that the dGATAb factor binds to three target sites flanking an EcR/USP binding site in a 70-bp enhancer that controls the tissue and stage specificity of Fbp1transcription. We demonstrate that one of these sites and proper expression of dGATAb are required for specific activation of the enhancer in the fat body. In addition, we provide further evidence that EcR/USP plays an essential role as a hormonal timer. Our study provides a striking example of the integration of molecular pathways at the level of a tissue-specific hormone response unit.

ACKNOWLEDGMENTS

We are grateful to M. D. Brennan and J. Hu for the gift of the #Srp antibody, to P. Ramain for the gift of the #2B8 antibody, and to R. Reuter and K.-P. Rehorn for the gift of the srp cDNA and the UAS-srp Drosophila line. We thank R. Reuter, K.-P. Rehorn, Y. Engström, and U.-M. Petersen for helpful discussions and for sharing information during the course of this work. We thank F. Schweisguth and A. Kropfinger for critical reading of the manuscript and M. Sémériva for expert advice on pericardial cells and lymph glands in dissections of fat bodies.

V. Brodu is a predoctoral fellow of the Ministère de la Recherche et de l’Enseignement. This work was supported by grants to J.-A. Lepesant from the Association pour la Recherche contre le Cancer (grant 6294), the Ligue Nationale Contre le Cancer, and the Centre National de la Recherche Scientifique.